1. Field of the Invention
The invention relates to a mechanical heart valve for use as an artificial heart or heart support system or for use in artificial conduits as are implanted for a connection ofthe left cardiac chamber to the aorta.
2. Description of Related Art
An artificial mechanical heart valve is designed to release the blood flow in one direction and close it off in the reverse direction. In doing so it should clear an open cross section as large as possible, if the pressure upstream is greater than downstream. In this phase the occluder, the movable element ofthe mechanical heart valve, should offer as little resistance as possible to the blood flow. If this pressure relationship is reversed by the action of the heart, the mechanical heart valve will quickly close off this cross section to prevent backflow of a larger amount of blood.
The materials which are available for building this mechanical heart valve are much inferior to natural substances from which the body makes the blood-carrying components. Artificial materials can cause formation of blood clots which can hinder the function of the mechanical heart valve or also can close off blood vessels farther downstream. Besides material properties, these processes are furthermore also largely determined by the blood flow through the heart valve. Stagnation areas in which the blood moves only little or even circularly are especially disadvantageous. In technical terms these areas are flow separations and they form mainly when the flow cross section is widened or has recesses, edges and depressions. Also components which project into the flow, such as occluders, clips, axles or supports on their downstream side are associated with the danger of flow separation.
Numerous mechanical heart valves are known in which attempts are made to avoid flow separation by means of streamlined occluders.
Furthermore, mechanical heart valves are known in which the cross section in the area of their retaining ring decreases in the flow direction, so that in the area of the journal mounting accelerated flow prevails and thus the danger of flow separation is reduced. However, the area of accelerated flow extends only for a short region and does not include the entire area of the heart valve.
It is common to all these mechanical heart valves that the occluder during the flow-through phase is fixed in its angular position by stops. Usually the angle of attack of the occluder to the flow is so large that the flow separates on one side ofthe occluder and thus flow separation occurs.
It is furthermore common to all these known mechanical heart valves that flow separation on the rear edge of their retaining ring is inevitable because the flow cross section is widened here. The consequence is that all mechanical heart valves which are made of material which is not optimally compatible with blood are associated (this applies to all mechanical heart valves) with a certain rate of thromboembolic complications which then endanger the patient.
These mechanical heart valves have been developed for replacement of diseased natural hearts and are matched to the geometry of the natural flow channels found beforehand, for example, the aortic root. In artificial blood pumps on the other hand for the valves an anatomically defined geometry is not stipulated and the flow channels can be configured freely around the occluder. The same applies to conduits which are clinically used for a connection of the cardiac chamber to the aorta.